LMR400 vs RG8X

[WRDJ205]

Since it’s been a year and I’m still dabbling in GMRS I decided to splurge on 50’ of LMR400 to connect to the J-pole on a stick that I showed previously.  
 

It arrived today and I thought it was time to do a test.  This is just a relative comparison test.  
 

Checking the output of the radio I was getting about 9W as a baseline.  I connected the radio to the Surecomm with just a rubber ducky antenna on the antenna side recognizing that this is not a good combination but it was consistent for the testing.  

Using the RG8X I measured 1.37W at the end of the cable.  Next, I did the exact same test with the LMR400 and got 6.07W.  

I was surprised at the results so I did it again and saw the same.  I realize that the LMR400 is a better cable but I did not expect to see such a large difference.  

[WRYZ926]

RG8X has around 86% loss over 100 feet while LMR400 has around 48% loss over 100 feet. Plus the fact that the center conductor, insulations (dielectric) and shield braid are bigger with LMR400 which helps reduce loss.

@WRDJ205 your real world measurements are close to what most online coax loss calculators will show.

While a j pole is not the best antenna, they work just fine. I've seen enough home made UHF j pole antennas built from solid copper wire that works well. No they won't have as much gain as other designs but nothing wrong with a J pole.

[nokones]

You more than likely may have a little Itty bitty wire strand shorting out to one of the connectors. Get a multi-meter and attached a probe to the center conductor and the other probe to the outside of the connector and set the meter for a continuity check and you should have either "OL" or 0.00 ohms for a perfect assembly of the connector(s). If you get any reading other than the aforementioned, you have a short.

Or, your antenna is way out-of-band.  Check the antenna with an antenna analyzer to determine the frequency center resonance.

Who assembled the connectors? Where did you purchase thd LMR400 cable from?

My first recommendation is scrap the J Pole and get a real professional grade antenna such as a Laird, Larsen, etc. and tune it accordingly.

[SteveShannon]

1 hour ago, WRYZ926 said:

WRDJ205 your real world measurements are close to what most online coax loss calculators will show

This!  Absolutely nothing unusual about the results.